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Modem Programming
Serial port
RS232 Hardware

DCB sructure detects the management settings for the serial port of the connection device.

DCB structure contains the following members:

DWORD DCBlength - sizeof(DCB)

DWORD BaudRate - baud rate. There is a standard set of : all the rate constants look like CBR_


E.g. CBR_9600, CBR_115200.


DWORD fBinary - Eof character check mode � Windows doesn't support this mode (at least now). Mask $01

DWORD fParity - Parity control Mask $02 � enabling Parity control

DWORD fOutxCtsFlow - Mask $04 � enabling CTS signal control at bytes output.

DWORD fOutxDsrFlow - Mask $08 � enabling DSR signal control at bytes output.

DWORD fDtrControl - Mask $30 � DTR signal control type: values

  • DTR_CONTROL_DISABLE - signal deactivation.
  • DTR_CONTROL_ENABLE - the particular signal value can be specified via calling EscapeCommFunction.
  • DTR_CONTROL_HANDSHAKE - automatic sygnal management.

DWORD fDsrSensitivity - Mask $40 - enabling DSR signal control.

DWORD fTXContinueOnXoff - XOFF continues Tx

DWORD fOutX - Mask $100. Enabling XON XOFF out flow control

DWORD fInX - Mask $200 -//- when receiving

DWORD fErrorChar - Mask $400. Allowing to replace the received byte with a ErrorChar structure member if the reception was erratic (parity mismatch occurred).

DWORD fNull - Mask $800 enable null stripping � skip NULL characters when receiving

DWORD fRtsControl - Mask $3000. Control type:

  • RTS_CONTROL_DISABLE - signal deactivation.
  • RTS_CONTROL_ENABLE - the peculiar signal value can be specified via calling EscapeCommFunction.
  • RTS_CONTROL_HANDSHAKE - automatic signal management
  • RTS_CONTROL_TOGGLE � high level while there's data to be transmitted .

DWORD fAbortOnError - Mask $4000. Abortion of read/write operations if errors occur

DWORD fDummy2 - Not used

Other structure data

WORD wReserved - Not used

WORD XonLim - min number of bytes in the receiving buffer before the XON character is sent

WORD XoffLim - min number of bytes in the receiving buffer before the XOFFcharacter is sent

BYTE ByteSize - number of bits in a byte is from 4 to 8

BYTE Parity - 0-4=no,odd,even,mark,space parity bit,

BYTE StopBits - 0,1,2 = 1, 1.5, 2 � stop bits, 1,5 used only when 5 bits are sent to 8250 chip.

  • ONESTOPBIT - 1 stop bit
  • ONE5STOPBITS - 1.5 stop bits
  • TWOSTOPBITS - 2 stop bits

char XonChar - Tx and Rx XON symbol

char XoffChar - Tx and Rx XOFF symbol

char ErrorChar - Symbol replacing the byte received by mistake

char EofChar - end of input character

char EvtChar - received event character

WORD wReserved1 - Not used

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